Electronic welding stations, such as those disclosed in U.S. Pat. Nos. 4,301,355 to Kimbrough et al., 4,349,720 to Makimaa, 4,409,465 to Yamamoto et al., 4,427,874 to Tabata et al., and 4,716,274 to Gilliland, generally have two output terminals, one of which is a direct connection to the DC power supply, and the other of which is connected to the power supply through a switching transistor and other components. Generally, the welding torch is connected to the switched output terminal. If only a single welding station is being used or if each welding station of a multitude of welding stations has an independent power supply then the polarity of the welding torch, with respect to the workpiece, can be selected by connection of the welding torch connector to, as desired, the positive output terminal or the negative output terminal of the welding station, and by connection of the workpiece to the other output terminal. However, when multiple welding stations are operated from a central power supply, such as disclosed in U.S. Pat. No. 4,716,274, simple reversal of the welding torch and workpiece connections on all of the welding stations will not achieve the desired result because the workpieces, which are generally interconnected, are connected to the switched output terminals. The result is that the switched output terminals are all operating in parallel and the desired control over the welding operation cannot be achieved. Therefore, there is a need for an electronic welding station which can be configured so that a selected one of the welding torch and the workpiece can be directly connected to the central power supply and the other connected via the switching transistor.
Electronic welding stations, such as those described in the above mentioned U.S. patents, generally provide a unipolar output. That is, the output of the electronic welding station is DC or pulsed DC and is always of the same polarity. These electronic welding stations do not provide an AC output. However, an AC output is desirable, especially for aluminum-TIG (tungsten inert gas) welding. Therefore, there is a need for an electronic welding station which can provide an AC output.
AC welding stations have been designed but it has been necessary to have both a conventional DC welding station, with its DC output, and an AC welding station, so that aluminum-TIG welding can be performed. This doubles the number of welding stations, which greatly increases the total cost and complicates maintenance and logistics. Therefore, there is a need for an electronic welding station which can provide either a DC output or an AC output, as selected.
In an electronic welding station which can perform both DC and AC welding operations it is desired to maximize the number of components that are used for both DC operations and AC operations and to minimize the number of components, especially larger and/or more expensive components, that are used for only one mode of operation. It is therefore desirable to be able to use the output inductor in a DC output welding station, for the transformer in an AC output welding station. However, the open construction of a typical inductor core generally provides insufficient coupling for use as a transformer and the closed construction of a typical transformer core provides too high an inductance for use in most DC-output welding operations. Therefore, there is a need for a component which can be selectively configured to operate as either an inductor or as a transformer, as required for the particular operation to be performed.
In conventional DC output electronic welding stations, the switching transistor is either in an on state wherein the full power supply voltage is applied to the switched output terminal, or in an off state wherein the power supply is isolated from the switched terminal. In these welding stations, the welding current is controlled by varying the pulsewidth (the on time of the switching transistor). However, this technique is generally not applicable to AC output welding stations since changing the pulsewidth for one polarity of the output waveform causes an opposite change in the pulsewidth of the other polarity of the output waveform. Therefore, the full power supply voltage, of one polarity or the other, would always be applied to the output terminal. Therefore, there is a need for a method for controlling the welding current of an AC output electronic welding station.
Electronic welding stations, in order to reduce manufacturing and maintenance costs, generally use a bank of switching transistors, rather than a single switching transistor. Some of the transistors will be easily accessible and, in the event of failure, can be easily replaced. However, some transistors will not be as accessible and, in order that replacement may be accomplished, the entire bank of switching transistors may have to be removed and/or other components or circuits of the electronic welder may have to be removed. In the latter case, a substantial amount of time may be required to replace the defective transistor, thus increasing the maintenance costs, and the removal of components other than the one which is to be replaced provides an increased occasion for misassembly and subsequent destruction of the electronic welder. Therefore, it is highly desirable to design an electronic welding station so that a transistor which fails is preferably a transistor which is easily replaced.
For a specified weld type, gas type, gas flow rate, welding rod material and diameter, torch travel speed, and work material type and thickness, there will be a range of values for the pulse frequency, a range of values for the pulsewidth, and a range of values for the wire feed speed that will produce an acceptable weld. Of course, for cost and efficiency reasons, it is desirable to perform a welding operation as rapidly as is possible while still producing a quality weld. To achieve this, wire feed speed and arc current should generally be at the high end of the allowable range of values, subject, of course, to adjustment based upon the skill of the individual welder. Some electronic welding stations have a plurality of accessible controls so that the wire feed speed, the pulse frequency, the pulsewidth (and the arc current), etc., can be individually varied. Other electronic welding stations try to sense the arc current or the arc voltage and adjust the wire feed speed and other parameters so as to maintain a constant arc current or arc voltage or respond to the arc current or arc voltage. However, the first type of electronic welding station cannot be rapidly adjusted because the operator may have three to five knobs to reposition while trying to obtain the desired arc. The second type of electronic welding station frequently produces less than desirable results because some of the parameters are not a precise function or a linear function of the arc current, the arc voltage, any particular individual factor, or any particular group of factors. Therefore, there is a need for an electronic welding station which minimizes the number of parameters that the operator has to select and which adjusts other dependent parameters so as to produce an optimum weld in light of the parameters selected by the operator.
It is desirable to monitor the arc voltage to determine whether the arc has been struck so as to allow the electronic welding station to use one set of parameters which are desirable for striking an arc and to use another set of parameters which are desirable for conducting the welding operation. Therefore, it is desirable to provide an arc detection circuit which operates with electronic welding stations which provide both positive ground and negative ground DC outputs and AC outputs.